In certain installations, it is necessary to preclude a machine or an apparatus from syphoning water back into the machine. For example, an automatic washing machine is connected to the hot and cold taps in a laundry tub. Also, the automatic washing machine has a discharge line which connects with the drain. Normally, the automatic washing machine is placed close to the laundry tub and the hot and cold taps. A pipe or tube runs from the laundry tub to the drain. With the automatic washing machine and the overflow for the laundry tub, both connecting with the drain, there is the possibility that the automatic washing machine may syphon some of the water in the laundry tub back into the washing machine. For example, many automatic washing machines have a suds-saver device whereby the discharge from the automatic washing machine can be introduced and stored in the laundry tub. Then, when it is desirable to wash a darker colored garment, the wash water in the laundry tub can be reintroduced into the automatic washing machine and used for washing the darker colored garment. For example, in the first wash there may be washed white clothes. The discharged water from washing the white clothes may be introduced into the laundry tub. After the white clothes have been washed, then light colored clothes and bath towels may be placed in the washing machine and the discharged water from the white clothes may be reintroduced into the washing machine for washing the light colored clothes and the bath towels. After the bath towels have been washed, the discharge water from this washing may be reintroduced into the laundry tub. Then, there may be washed dark color clothes, such as blue jeans and the like. The water in the laundry tub may be reintroduced into the washing machine for washing the dark color clothes. The result is a saving in hot water as the hot water from the washing machine can be reused and also there is some saving in washing agent or cleaning agent. Unfortunately, once in a while the washing machine, on a rinse cycle, may syphon off or suck into the washing machine some of the waste water from a previous washing. The introducing of the waste water into the washing machine with rinsed clothes may stain the clothes or may contaminate the clothes and get the clothes partially dirty. With this problem in mind, I have devised the subject invention.